Add negative binomial distribution

[guilhermebodin]

No description provided.

[codecov]

Codecov Report

Merging #99 into master will increase coverage by 0.02%.
The diff coverage is 86.20%.

@@            Coverage Diff             @@
##           master      #99      +/-   ##
==========================================
+ Coverage   89.79%   89.81%   +0.02%     
==========================================
  Files          29       30       +1     
  Lines         686      707      +21     
==========================================
+ Hits          616      635      +19     
- Misses         70       72       +2     

Impacted Files	Coverage Δ
src/ScoreDrivenModels.jl	100.00% <ø> (ø)
src/distributions/common_interface.jl	100.00% <ø> (ø)
src/opt_methods/common_methods.jl	100.00% <ø> (ø)
src/univariate_score_driven_recursion.jl	88.23% <ø> (ø)
src/MLE.jl	96.61% <83.33%> (ø)
src/distributions/negativebinomial.jl	85.00% <85.00%> (ø)
src/distributions/chi.jl	76.47% <100.00%> (ø)
src/simulate.jl	100.00% <100.00%> (ø)
... and 1 more

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